This proposal will study human IEL: their adherence to adjacent cells [mesenchymal cells of the basement membrane and epithelial cells (EC) or EC tumors) and the divergent effects after activation through the CD2 and CD3 pathways. The IEL, located in the epithelium, between the myriad antigens in the lumen and the lymphocyte-rich lamin propria, are likely to be important in the regulation of the intestinal immune response. Although the functions of this lymphocyte compartment are largely unknown, those studied by this laboratory proved to have unique features. The logical extensions of this work, ad delineated in this proposal, will greatly add to an understanding of the biology of these cells. Study of the ADHESION OF IEL TO MESENCHYMAL CELLS AND TO EC TUMORS will be divided into three parts. Analysis of IEL binding to mesenchymal cells will be the identification of surface molecules involved as well as delineation of the conditions necessary for this interaction to occur. Analysis of IEL binding to EC tumors will be the development of monoclonal antibodies to the ligand to alphaEbeta7 (HML-1) on EC tumors as well as a determination as to whether alphaEbeta7 and CD11a are closely associated on IEL. (These molecules are responsible for binding of IEL to EC tumors). Finally, the chemotaxis of IEL toward cells and soluble factors in their environment will be assessed. Study of IEL ACTIVATION THROUGH THE CD2 AND CD3 PATHWAYS will be divided into seven parts. Those IEL subsets that proliferate in response to stimuli of each pathway will be identified by bromodeoxyuridine incorporation. The association of surface structures, such as CD8, CD45, and alphaEbeta7, with CD2 and CD3 will be determined by immunoprecipitation and immunoblotting. The possibility that stimulation through the CD3/TCR complex induces apoptosis by IEL will be evaluated using flow cytometry and ethidium bromide gels. The point at which stimulation of IEL through the CD2 and CD3 pathways diverge will be identified by analyzing activation events (calcium influx and phosphoinositide turnover) and post-activation events (effect of IL-4 on IL-2-induced proliferation). Analysis of the mechanism of the enhancement of IEL activation by mesenchymal cells will include identification of surface markers involved and the ability of IEL to affect mesenchymal cell activity, since cell-cell interactions are often bidirectional. The roles of alphaEbeta, and CD1 on IEL function will be analyzed. Finally, lymphokine production by IEL will be measured (using bioassays and Northern analysis) after CD3 activation in the presence or absence of mesenchymal cells and EC, since soluble products are likely to be essential in cell-cell communication. The IEL have unique phenotypes, functions, and environmental stimuli. Their location suggest their role as regulators of the intestinal immune response. Understanding the mechanisms of two basic functions (adhesion and activation) of IEL in the normal state will help in understanding the pathogenesis of inflammatory diseases.